Proteins of the ADAR (adenosine deaminases acting on RNA) family catalyze the most common RNA editing event in mRNA in human cells, A to I deamination. ADAR specifically edits residues in regions of double stranded RNA. ADAR activity results in selective editing in shorter, imperfect stems, whereas long perfectly double stranded regions are usually more extensively edited. ADAR activity plays an important physiological role and has been implicated in cancer, development and RNAi. ADAR proteins have also been shown to be important factors in the replication of many viruses. However, only a few studies to date have dealt with the effects of ADAR genes on HIV replication. The effects of ADAR1 on HIV1 remain controversial, with reports of both positive and negative effects, whereas there is only one published study of the effects of ADAR2. The molecular mechanism underlying ADAR effects remain to be elucidated. The ADAR genes were likely generated from a common ancestor that also gave rise to another family of editing enzymes, the ApoBec proteins. These proteins have recently been proposed to potentially play a role in HIV evolution and immune evasion, in addition to their roles in HIV restriction. Our hypothesis is that ADAR proteins are also used by HIV, not only for regulation, but also for evolution and immune evasion. We thus propose to initiate studies to systematically and extensively analyze the effects of ADAR on HIV. First we will determine how ADAR edits stem regions in the HIV mRNAs and how this relates to RNA trafficking pathways. Secondly, we will analyze ADAR editing of HIV sense/antisense RNA hybrids, using a therapeutic HIV antisense RNA as a model. Specific Aim 1: To analyze how ADAR1 and ADAR2 function to edit stem-loop regions in HIV mRNAs and if differential editing occurs depending on the mRNA export pathway. Specific Aim 2: To analyze how ADAR affects antisense RNA mediated inhibition and RNA editing in HIV antisense target regions.